Processing of benzene hexachloride alcoholic solutions



United States Patent PROCESSING OF BENZENE HEXACHLORIDE ALCOHOLIC SOLUTIQNS Leo Danzker, Kenmore, N. Y., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia N0 Drawing. Application April 4, 1952 Serial No. 280,650

4 Claims. (Cl. 260-648) is chlorinated to obtain a mixture of isomers of benzene hexachloride, usually containing about -15 percent of the gamma isomer, the remainder being composed of other isomers, primarily alpha and beta isomers. Only the gamma isomer is insecticidally active and, therefore, it is advantageous to separate it from the other isomers present for use as an insecticide. For this purpose various solvents have been used including benzene, aliphatic hydrocarbons, chlorinated aliphatic hydrocarbons and alcohols, particularly methanol. The latter are most effective and are widely used for extraction of the gamma isomer from crude benzene hexachloride or for recrystallization of the crude product.

In the chlorination of benzene, which is usually carried out under anhydrous conditions, corrosion is not a serious problem. However, in alcoholic extraction or crystallization processes, even though carried out under substantially anhydrous conditions, corrosion of the common metals of construction is severe, particularly at high concentrations of benzene hexachloride, or of the gamma isomer, and at high temperatures. Corrosion resistant materials of construction may be used, such as glass or graphite, but they are fragile and diflicult to install and maintain. Some corrosion resistant alloys may also be used but they are expensive and diflicult to fabricate. The more common corrosion resistant alloys such as 304 and 316 stainless steel cannot be employed.

It is important to avoid corrosion not only because of equipment cost and fabrication problem but also in order to prevent contamination of the benzene hexachloride. Moreover, the corrosion products of many of the metals of construction catalyze the dehydrochlorination of benzene hexachloride. This further contaminates the product, reduces insecticidal activity of the mixture, and in the manufacture of lindane, a composition containing at least 99 percent of the gamma isomer, yields may be materially reduced.

I have found that the addition of a relatively small proportion of a nitrate of an alkali or alkaline earth metal to alcoholic solutions of benzene hexachloride greatly inhibits the corrosion of the common metals of construction such as stainless steels, copper and copper alloys. Surprisingly the metal nitrate does not separate as a solid when lindane or the gamma isomer concentrates are produced by concentration and crystallization of the alcoholic solutions although it might be expected to do so due to its limited solubility in alcohol. Moreover, I have found that gamma isomer concentrates obtained from alcoholic solutions containing metal nitrates have better color and less objectionable odor than products obtained from nitrate-free solutions. Moreover, an increase in yield, seems to result. The insecticidal properties of lindane or gamma isomer concentrates produced according to my invention are unimpaired.

The nitrates useful in the process of my invention are alkali and alkaline earth metal nitrates. Sodium nitrate, being effective and readily available, is preferred. Other nitrates, such as potassium and calcium nitrates, are also useful. Relatively small proportions of the nitrate are required to effectively inhibit corrosion, for example, about 0.5 weight percent of sodium nitrate based on the alcohol content gives very satisfactory protection and as little as about 0.05 weight percent produces a significant improvement. However, ranges of from about 0.05 to 2 weight percent or more may be used if desired.

The benefits of my invention are particularly marked with the common and relatively available 18-8 stainless steels Nos. 304 and 316 which ordinarily are particularly susceptible to corrosion by alcoholic solutions of benzene hexachloride. Hence these materials are made available for this service. Copper and copper alloys are surprisingly protected from corrosion by the vapor above the nitrate inhibited solutions. Although ordinary carbon steel is severely attacked by relatively dilute solutions of benzene hexachloride in methanol, for example, at the boiling point, about 2 weight percent of sodium nitrate in the solution reduces the corrosion rate to less than 4 percent of that observed in the absence of the inhibitor.

The following table shows corrosion tests on various metals with nitrate-free and nitrate'containing methanol solutions of benzene hexachloride. In the table, column 1 shows the metal tested, column 2 shows the percent of sodium nitrate based on the methanol, column 3 shows the corrosion rate in inches per year, column 4 shows the concentration of benzene hexachloride (BHC) in the methanol solution and columns 5 and 6 give the exposure time in hours and the temperature of the solution in degrees centigrade. All the tests were of sufiicient duration to give reliable and reproduceable results.

NaNOs, Cor- BHO Expo- Metal weight rosion cone, sure, Temp.,

percent rate, perhrs. 0.

inlyr. cent 0 1 6 25 140 G6 0. 5 0 022 25 275 66 Stainless steel, N0. 304" 1.0 None 25 230 66 O. 5 0 083 45 230 68 0. 5 0 93 174 0 0 12 25 165 66 0. 2 0. 059 25 165 66 0. 5 0. 004 25 230 66 0.8 None 25 230 66 Stainless steel, No. 316.- 1.0 0.006 165 66 0 0. 094 45 68 0. 5 0.0037 45 230 68 0 0.002 90 140 110 8. 5 (2125 )90 1% 118 l 11 "i 0. 5 0. 034 174 110 O 5.2 25 4g 26 0. 5 2. 25 4 6 can) Steel H 1. 0 1. 1 25 230 66 2.0 0. 18 25 66 1 Exposed to vapor above a 90% BHC solution in methanol at 110 C.

The table shows that about 0.5 percent of sodium nitrate based on the alcohol reduces the corrosion rate to tolerable limits. Even greater reductions may be obtained by the use of larger proportions of sodium nitrate.

Thus, my invention provides an eifective and inexpensive means of inhibiting corrosion of the more common and cheaper metals desirably employed in the construction of equipment for the manufacture of benzene hexachloride or for the extraction of the gamma isomer from crude benzene hexachloride with resulting savings in capital investment and/or maintenance costs. Product Patented Aug. 26, 1958 4 nitrate is added in an amount of about 0.5 to 2.0 percent by Weight based on the alcohol content of the solution.

3. A process according to claim 1 in which the metal nitrate is sodium nitrate. 5 4. A process according to claim 1 in which the alcoholic solution is a methanol solution.

References Cited in the file of this patent UNITED STATES PATENTS Bayes Apr. 11, 1939 Whaley et al Apr. 23, 1940 

1. IN A PROCESS FOR THE REFINING OF BENZENE HEXACHLORIDE WHEREIN THE BENZENE HEXACHLORIDE IS PRESENT IN ALCHOLIC SOLUTION IN CONTACT WITH A METAL SUBJECT TO CORROSION BY THE ALCOHOLIC SOLUTION, THE STEP WHICH COMPRISES ADDING TO THE ALCOHOLIC SOLUTION A NITRATE OF A METAL SELECTED FROM THE GROUP CONSISTING OF ALKALI METALS AND ALKALINE EARTH METALS IN AN AMOUNT SUFFICIENT TO INHIBIT THE CORROSION. 